The present invention relates to weaving looms and, more particularly, to a weft-yarn drawing-off and length-measuring apparatus for use in a weaving loom of the type in which the weft yarns of different natures, typically of different colors.
The weft-yarn drawing-off and length-measuring apparatus of this character use a combination of a length-measuring roller rotatable about a fixed axis and a pressing roller which is in rolling contact with the length-measuring roller and which is rotatable about an axis parallel and movable with the axis of rotation of the length-measuring roller. The length-measuring roller is driven at a constant speed in synchronism with other driven units of the loom so that a weft yarn passed between the length-measuring and pressing rollers, in rolling contact with each other, is drawn off successively in predetermined length from a yarn package.
Such a weft-yarn drawing-off and length-measuring apparatus is used in combination with program-controlled weft control means adapted to deliver a mechanical weft-change signal for causing the drawing-off and length-measuring apparatus to move the weft yarn between a position or direction passable between the length-measuring and pressing rollers and a position or direction deviated from the position passable between the rollers.
The measured length of weft yarn is picked in a suitable manner into the shed of warp yarns and forms a fell at the edge of a woven fabric during each cycle of operation of the loom, as is well known in the art. The length in which the weft yarn is drawn off through the length-measuring and pressing rollers in each cycle of operation of the loom determines the width of the woven fabric and is dictated by the diameter of the length-measuring roller which is in use. The length-measuring roller is thus arranged to be exchangeable with another length-measuring roller having a different diameter so as to permit selection of the width of a fabric to be woven.
When the length-measuring roller is exchanged with another roller having a larger or smaller diameter, the pressing roller carried on the new length-measuring roller is curvilinearly moved in an arc upwardly or downwardly from the original position thereof. This results in a change in the position or direction of the weft yarn relative to the line of contact between the rollers and it frequently happens that the weft yarn is moved out of the position or direction passable between the rollers. To remedy such a condition, laborious and meticulous efforts are required for the re-adjustment of the guide means retaining the weft yarn.